1. Field of the Invention
The present invention relates to electroacoustic receivers/transmitters, and in particularly to earphones/microphones that receive and transmit sounds.
The present application claims priority on Japanese Patent Application Nos. 2010-39296 and 2010-263676, the content of which is incorporated herein by reference.
2. Description of the Related Art
Earphones/microphones (or earphone microphones) have been developed and widely used as optional devices of mobile phones (or cellular phones) allowing users to conduct hand-free conversations with counterpart ones. Earphone microphones can be designed such that miniature microphones are embedded in earpieces inserted into external auditory canals of users' ears, wherein miniature microphones receive sounds transmitted inside external auditory canals via skulls (see Patent Document 1). When earpieces are inserted into external auditory canals so as to close external auditory pores, surrounding noise occurring externally of external auditory pores are hardly transmitted into external auditory canals. Those earphone microphones are able to transmit sounds precluding surrounding noise occurring outside users' ears.
Patent Document 1: Japanese Patent Application Publication No. 2007-281916
While sounds produced by vocal cords are being transmitted to external auditory canals via skulls, specific frequency ranges prerequisite for discriminating consonants of human speeches, e.g. frequency components of 3 kHz or higher, are being canceled/attenuated. Even when talkers' sounds transmitted inside their external auditory canals are transmitted to counterpart listeners/talkers over phones, it is difficult to conduct smooth conversations due to loss of frequency components prerequisite for discriminating human speeches.